System for keying transmitters



Oct. 18, 1932. I w, MOSER 1,882,862

SYSTEM FOR KEYING TRANSMITTERS Filed Jan. 13, 1926 *I I I I I P INVENTORWILHELM M05ER A ORNEY Patented Oct. 18, 1932 WILHELM MOSER, OF BERLIN,GERMANY, ASSIGNORTO TELEFUNKEN GESE LLSCHAFT FUR DRAHTLOSE TELEGRAPHIEGERMANY I o1" BERLIN, GE MA Y, A CORPORATION F SYSTEM FOR KEYINGTRANSMITTERS Application filed January 13, 1926, Serial No. 80,926. andin Germany March 7,1925.

The keying of tube transmitters for short waves is attended with anumber of difficulties which manifest themselves upon the reception ofsuch waves. In beat reception, for example, a far higher wave constancy1s necessary than when working with longer waves. F or instance, if a30-meter wave unclergoes a variation of only 9 th of one percent thismeans that the frequency (10 per second) will change by 10,000oscillations per second. The beat tone is subject to fluctuation by anequal amount, with the result that proper sound-reading reception isrendered extremely difiicult.

It has been found that changes in the wavelength inside the said orderof magnitude are associated with every change in energy of thetransmitter tube. Consequently a keying method that would suggest itselfcan be exressed: ke in si nal=full ener k-e in p y D b O intermission=noenergy, which method is readily applicable in connection with longwaves, but is useful for short-wave work only when the operating meanssupply full energy also during the intermissions, in which instance thesame must be destroyed by an add tional element or means. This resultsin a considerable enlargement and an increase in cost of apparatus.

The same end may be attained in a simple manner by detuned keying, inthe presence of perfectly constant, or substantially perfectly constantenergy. In the case of short waves, this method is especially suited forthe reason that the wave variation has to be only very small in order tofurnish a change in frequency suilicient for the reception of the keyedsignals. 0

In telegraphic work on short waves it has been discovered that undampedtelegraphic signals, to be sure, can be transmitted to very greatdistances, but that it is difiicult to locate the transmitting stationin heterodyne reception, or to re-locate it after it has been lost onaccount of fading or atmospherics. It is well known that this difiicultyis not quite so great in the case of damped or modulated signal work.

However, in the case of modulated transmission, the question comes upagain as to ing signals are modulated what the most suitablekeyingmethod would be. The most correct method of keying is that fromzero to full energy. However, since also in this'cas-e highwave-constancy is requirechprovisions must be made for an equalizationof load to which reference was made above. If this complication isavoided, it is possible to work similarly as in the case of continuouswave work with detuned key- 'ing,'except that here the changes in thewaves must be incomparably larger than with continuous wavetransmission. The transmltter requires a by far'larger placeln the fre'quency scale. 7 I

Now, the present invention discloses a new keying method adapted tosolve the problem.

According to the invention, the modulation of keying signals and keyingintermissions is chosen difierently in such a way that thekeying-signals possess a definite-mode ofm'odelation from one key signalto'another, while the keying intermissions have another mode ofmodulation which is the same for each keying intermission.

The method may be practiced with either termissions as different aspossible fromthat of the keying'signals for instance, the intermissionsneed not be modulated at all, that is to say, are sent und'amped, whilethe keying signals are modulated to the fullest extent or the inverseplan could be followed. I

' *Another method resides in that the modulation frequencies are chosento be of difierent values, for instance, the key signals couldbe'modulated at a'frequency of 2000, while 7 .tlieint'ermissionscouldbemodulated at a he 9 quency of '200, or the int e zrmissions' could bemodulated at some inaudible frequency. The method hereinbefore indicatedcould be combined'rea'dily with the detuning of the wave-lengths. Inthis manner thebest possible separation and differentiation between keydash, and space or keying intermission could be obtained.

In the following, a number of embodiments and arrangements adapted tothe practicing of the method shall be described by way of example.

Fig. 1 shows an arrangement in which the degree of modulation isutilized.

Fig. 2 shows a diagram of connections whereby the signal or theintermission may be modulated.

Fig. 3 shows an arrangement whereby the frequency is modulated.

Fig. 1 shows an arrangement in which the degree of modulation of keyingsignals and keying intermissions is chosen so as to be of differentvalue. The transmitting apparatus consists of a separately controlledtube transmitter comprising the oscillator tube S and the modulator tubeH which operates upon the aerial A. The grid of the tube H is shut offfrom the couplingcircuit by the aid of the blocking condenser E. Thegrid direct current flows through the choke coil D1, connecting pointsor terminal G, and resistance R1 to terminal K, and from there by way ofchoker D2 to the heated filament. Modulation is efiected by way of thetransformer T1" which is connected in parallel with relation to theresistance R1, and which consequently imparts to the grid of the maintransmitter an additional alternating current component of the desiredfrequency. For the purpose of variation of the degree of modulation, aresistance R2 is inserted between Tr and R1 which may be short circuited by the telegraph key T. It will be understood that when R2 isshort-circuited the degree of modulation is naturally higher than whenthe key is open. Fig. 2 shows the direct current path and GK of the gridin the case where the keying signals are non-modulated and the keyingintermissions modulated, or vice versa. The key is here dis osed inparallel with reference to resistance 1, and therefore parallel to themodulating transformer Tr. By closing the key, modulation ceases.According to whether the key is arranged to operate as a working oras aback contact, either the signals or the spaces will be modulated. Fig. 3shows an arrangement which makes it possible to choose the modulationfrequency of keying signals and intermissions of different frequencieseither of radio or audio frequencies. The grid direct current flows herefrom point G through the series-connected resistances R1 and B2. Inparallel relation to R1 is a transformer Trl, and in parallel to R2 atransformer T122, transformer Trl serving to transfer frequency N1 andT72 to transfer frequency N2. By means of key T provided with a workingand a back contact, alternately the one or dered inoperative. Hence,according to the mode of connection it is possible to use either the oneor the other frequency for the signals or for the spaces.

Having fully described my invention, what I claim is 1. in atransmitting system, a source of high frequency oscillations having itsoutput electrodes connected with a load circuit,

a thermionic modulator tube, means for impressing oscillations from saidhigh frequen- WILHELM MOSER.

he' the in tru t Q te en-

